(1) Field of the Invention
This invention relates to an improvement in a positive type photosensitive material and to a process for developing the same, and more particularly to a photosensitive material which is able to form an excellent color-developed positive relief image by developing the exposed photosensitive material with an aqueous alkali solution and washing it with water. The invention also relates to flexible and tough image film which can be stripped off from a base material as occasion demands, as to well as a process for developing the same.
(2) Description of the Prior Art
In the past, the following processes have been employed to obtain a positive relief image using ultraviolet rays as a light source.
(1) A layer of photosensitive composition consisting of a o-quinonediazide derivative and alkali soluble resin binder (e.g. novolak resin) is formed on a base material to obtain a photosensitive reproduction material. The photosensitive reproduction material thus obtained is exposed and the exposed areas are alkali-developed.
(2) A layer of photosensitive composition consisting of a reaction product of p-diazodiphenylamine with phosphotungstic acid and a vinylidene chloride-acrylonitrile copolymer binder is formed on a base material to obtain a photosensitive reproduction material. The photosensitive reproduction material thus obtained is exposed and the exposed areas are developed by using a water-alcohol solution (see Japanese patent publication No. 42-14326, claiming priority of U.S. Appln. Ser. No. 345,848 filed Feb. 19, 1964).
(3) A layer of photosensitive composition consisting of an ethylenically unsaturated compound, a thermoplastic polymer, a photopolymerization initiator, and a dye or pigment is formed between two sheets of supports to obtain a photosensitive reproduction material. The photosensitive reproduction material thus obtained is subjected to development/peel procedure utilizing the change of adhesive strength in the exposed areas, and a relief image is formed by the remaining photosensitive composition (see U.S. Pat. No. 3,060,023).
(4) A positive relief image is obtained by using a photoresist composition containing as main components an o-quinonediazide compound and an alkali-soluble vinylic polymer compound having phenolic hydroxyl groups and represented by the general formula: ##STR1## wherein R represents hydrogen, hydroxyl, carboxyl, alkyl, alkoxyl, aryl, nitro, amino or halogen (see Japanese patent publication No. 50-8658).
However, these prior art processes have the following disadvantages and are insufficient to obtain images having high density and high resolving power.
With regard to the above-mentioned process (1), the binder resin can be dyed only with difficulty. Further, it is difficult to combine the binder resin with an efficient color developing mechanism. For this reason, a dye or pigment is usually dispersed in the binder resin and in order to obtain high light shielding density, a long period of exposure is necessary and therefore, impractical.
In the above-mentioned process (2), high light shielding density can be obtained without decreasing sensitivity by providing a light shielding layer on the photosensitive layer which is formed on a transparent base material, but in this case exposure can be made only from the transparent base material side and a decrease in resolving power due to the thickness of the base material is unavoidable.
Further, the above-mentioned process (3) has the same disadvantage as the process (2), because exposure is made through the transparent base material. Besides, since development is made by agglutination and destruction of the photosensitive layer, resolving power is reduced. Another disadvantage in the process (3) is in that the price of the photosensitive material is high.
The above-mentioned process (4) can give a positive relief image by alkali-development, but it has a disadvantage that no color development is observed and no image having high density can be obtained.